System for conserving liquefied gases



May 1, 1951 H. E. THOMPSON Filed Feb. 12, 1947 SYSTEM FOR CONSERVINGLIQUEFIED GASES 2 Sheets-Sheet l ggggffgi-fe 42 52 50 5/ T0 ATMOS. 22' v47 v v v 46 45 V 44 5.4 A g 52 56 3g 6/ 54 v Rsssue/A/c LINE 5/ kDISCHARG/NG LINEgO a 3 3 VAPOR LINE J CHARGING 1.1/35 j 77 1 v fl klfmlylmlfllwlvlllllnlfllfi 'wmmmmnvrII lg INVENTOR HAROLD E. THOMPSON 442 1. BY 2E ATTORNEY 2 Sheets-Sheet 2 H. E. THOMPSON SYSTEM FORCONSERVING LIQUEFIED GASES N Am MUWQ May 1, 1951 Filed Feb. 12, 1947 MEDQOQVA INVENTOR HAROLD E. THOMPSON ATTORNEY Patented May 1, 1951 SYSTEMFOR CONSERVING LIQUEFIED GASES Haroid E. Thompson, Rye, N. Y., assignor,by

mesne assignments, to Union Carbide and Carben Corporation, acorporation of New York Application February 12, 1947, Serial No."128,072

This invention relates to a system for conserving liquefied gases andmore particularly to a system for the economical marine transportationof liquefied hydrocarbons and for conserving such gases during shipment.Large quantities of propane are now either wasted or are unavailable foruseful purposes due to the lack of a satisfactory and economical methodof large bulk transportation of such gases.

Liquefied hydrocarbon gases such as propane, propylene, butane and thelike are commonly stored and transported in closed pressure vessels atatmospheric temperatures. It is necessary in accordance with marineshipping regulations that such pressure vessels shall be designed forworking pressures equal to the vapor pressure of the liquefied gas at amaximum summer temperature of 115 F. At such temperatures propane, forexample, has a high vapor pressure of 213 p. s. 1. gauge and arelatively low liquid density (3.83 pounds per gallon). It is furtherrequired that such containers shall not be com" pletely filled withliquid at the maximum working pressure and at 115 F. Thereiore, the

weight of metal in the vessels is high relative to the amount ofliquefied gas contained therein. Shipment by high pressure tank car isexpensive and involves high investment costs. The excessive steelrequirements have prevented the development of a satisfactory highpressure tank barge for the waterway shipment of liquefied hydrocarbongases. With propane as a cargo, for example, the design of a tank bargefor transportation at atmospheric temperatures would result inexcessively thick-walled pressure containers such that for a standardsize of barge, 195 feet long by 35 feet wide, the weight of steelrequired f 1 the pressure containers would be approximately 700 tons andthe weight of the empty containers and the barge would approximate 900tons, such that the useful carrying capacity for the propane cargo wouldonly be in the order of 300 tons.

Liquefied propane could be transported at atmospheric pressure if itstemperature were maintained at the boiling point corresponding toatmospheric pressure, which is 44.1'7 F. The maintenance of thistemperature, however, would require an excessive weight and thickness ofinsulation for the container or the evaporation loss would be high. Acertain minimum wall thickness for the container would still benecessary, particularly for a large container, merely to hold the weightof liquid cargo and for structural selfsupport. In order to preventlarge evaporation losses, the energy required for refrigerating theliquid would be so great as to be economically prohibitive. Greatdifificulties are also encountered in order to avoid pressure changeswhich large 5 Claims. (01. 62-1) tanks are not able to withstand unlessthe Walls are made heavy.

By the present invention these and other difficulties are overcome andlarge bulk shipment of liquefied hydrocarbon gas is economically carriedout by maintaining the cargo at moderate superatmosph-eric pressure andat a depressed temperature which is intermediate between the maximumsummer temperature and the boiling point of the liquefied gas atatmospheric pres-'- sure. The liquefied gas cargo is maintained at thedepressed temperature by a refrigerating system preferably involving theremoval of a portion of the vapor phase of the cargo from the shippingcontainer, compression of such vapor to a pressure sufiicient to permitliquefaction thereof by heat exchange with a suitable cooling medium,for example, the river or canal water during waterway shipment, andfinally expansion and readmission of the expanded gas ma terial into theshipping container. The maximum working pressure is chosen such that thewall thickness of the containers need be only slightly greater thanwould be required for structural strength to hold the liquid atatmospheric pressure. A moderate thickness only of insulation about thecontainer is necessary, and therefore the tare weight is proportionatelysmall compared to the weight of cargo. In addition to the advantage oflighter weight shipping containers, the maintenance of intermediatetemperature and moderate pressure provides conditions under which thedensity or weight per cubic foot of the cargo is considerably greaterthan when shipping the liquefied gas under high pressure, and thus agreater amount of liquefied gas can be transported in a given sizecontainer. At the same time refrigeration is not continuously requiredand the energy required for refrigeration when needed is relativelysmall. Large quantities of liquefied hydrocarbon gas can be transportedsafely for long distances with both a low investment cost and a lowtransportation cost and with immaterial gas loss.

The principal objects of the invention are, therefore, to provide amethod of and apparatus for conserving and shipping liquefiedhydrocarbon gases which maintains the cargo of liquefied gas at amoderately reduced temperature and a low superatmospheric pressure, suchthat the quantity of liquefied gas conserved and shipped is largerelative to the weight of its container, which permits large bulkshipments of liquefied gas with safety, with immaterial gas loss, andwith economy of investment and transportation costs; to provide such amethod and apparatus in which continuous production of refrigeration isnot essential and the amout of refrigeration which is required ismoderate, in which advantage may be taken of periods when atmospherictemperatures are low to eliminate the need for refrigeration, in whichthe cargo itself is employed in the refrigeration cycle and the energyfor the refrigeration production is furnished by a small portion of thecargo to eliminate the need for an independent refrigeration cycle and aseparate source of energy to operate same, and by which a large quantityof liquefied gas can be economically transported for long distances bywaterway and the cooling power of the water taken from the waterwayemployed to reduce the energy required for refrigeration.

The above and other objects and novel features of the invention willbecome apparent from the following description having reference to theannexed drawings wherein:

Fig. 1 diagrammatically illustrates an exemplary system for conserving aliquid hydrocarbon gas while being transported; and

Figs. 2 and 3 are respectively plan and and elevational views of a bargefor waterway transportation of liquefied gas.

The invention will be described particularly for the transportation ofpropane, but the principles thereof are adapted for the transportationof other combustible gases, for example, ethane, propylene, ethylene,etc. The pressures mentioned herein are to be understood as gaugepressures unless otherwise specified.

Propane has a boiling point at atmospheric pressure of ll.17 F. and avapor pressure at 115 F. of 213 p. s. i. The characteristic vaporpressure curve for propane is such that at increasing temperatures thechange in vapor pressure becomes increasingly greater, particularly atthe higher temperatures. It is, therefore, possible to effect a majorreduction of vapor pressure by the relatively moderate reduction oftemperature. For shipping propane according to the invention an upperpressure limit of p. s. i. is preferred and a normal operating pressurelimit is preferably chosen at 75 p. s. i. The boiling point of propanecorresponding to 100 p. s. i. is 64 F., and that corresponding to 75 p.s. i. is 43 F., and, therefore, no refrigeration would be required toprevent loss of gas by venting whenever the atmospheric temperature isbelow 64" F., as often occurs during the colder months.

To maintain the pressure at 75 p. s. i. no refrigeration would be neededwhenever the atmospheric temperature is below 48 F. If, however, thelarge container were designed for holding propane .at atmosphericpressure, the liquid would have to be maintained at a temperature of atleast 90 F. lower than an atmospheric temperature of 48 F. and it willbe seen that under such conditions the insulation heat leakage would belarge and the requirement for refrigeration would be continuous. Thus bydesigning the container for 100 p. s. i. maximum pressure instead of amaximum pressure of 213 p. s. i., a major reduction of wall thicknessand weight of container is effected and only an inappreciable amount ofrefrigeration is required. There also will be long periods when norefrigeration at all will be needed.

Even though the containers are designed fo 100 p. s. i. maximum pressurea further advantage results from maintaining a normal maximum operatingpressure less than 100 p. s. i. and preferably about '75 p. s. i., inthat it will take a long, time for heat leak during hot summerconditions to raise the pressure up to 100 p. s. i. if

the refrigeration device were inoperative for any reason, such as forminor repairs.

For providing the moderate amount of refrigeration when necessary, acompressor is arranged to draw vapor from the container or containersand to compress it into a condenser where it is liquefied by heatexchange with cooling water pumped from the waterway. The liquefiedvapors are expanded through a valve and passed into the container tocool the contents. The compressor and cooling water pump are preferablydriven by a gas engine which burn a portion of the vapor to provide thepower. Thus a portion of the cargo supplies the energy required for itsrefrigeration and the small portion of vapor used by the engineconstitutes the only loss of cargo during storage and shipment, whichloss is relatively immaterial in amount. For example, with a full bargeload of about 700 tons of propane, the fuel consumption may be only 0.2%

of the total cargo during a twenty-three day trip under hot summerconditions. A special fuel for the engine can be provided if it isdesired to avoid any loss of cargo.

Referring now to the drawings and particularly to Fig. 1, one of thelarge containers for holding liquefied hydrocarbon gases as indicated inschematic cross-section at H], the container [0 may have any suitableshape and is preferably cylindrical with hemispherical ellipsoidal orelliptical ends. The upper portion of the container in may be providedwith a dome H of customary construction to which various conduits may beconnected and, if required, two 01' more sealed manholes it may also beprovided. As indicated hereinbefore, the container It is constructed ofmetal which is thick enough to withstand internal working pressure of p.s. i. The container is covered with layers of heat insulation l3 and i4,and particularly when the container is mounted in a barge a layer ofinsulation l3 covering the lower half of the container may be thinnerthan the layer It covering the upper half of the container. The thickerinsulation covers the portion of the container above the main deck levelof the barge, which is subject to higher atmospheric temperatures andradiation from the sun. For example the layer I3 may be about two inchesof cork and the layer it may be about four inches thick.

A preferred assemblage of apparatus for refrigerating a body ofliquefied gas l5 held in the container is also diagrammaticallyillustrated in Fig. l. The liquefied hydrocarbon gas is filled into thecontainer I 6 through a charging line it, controlled by a valve ll andentering through the dome II. For discharging liquefied gas whendesired, for example at the destination, a discharge line is preferablyleads from a sump H9 at the bottom of the container IE] and upwardlythrough the dome II. This is controlled by a valve 20. Other auxiliarydevices of customary type are also provided such as a pressure reliefva1ve 2l, connected through the dome l l and set to discharge gas atpressures above 100 p. s. i., and liquid level indicating devices whichmay extend into the container at a manhole l2.

For drawing gas from the container a vapor line 22, controlled by avalve 23, connects to the gas space in the dome H and conducts gas fromthe container to the inlet 2d of a gas compressor 25. The compressedvapor is conducted from the conduit 2?. denser 26 passes from the lowerend thereof through a conduit 28 to the inlet of an expansion valve 29and from the discharge of the expansion valve 29 a conduit 30 conductsthe resulting expanded gas material through the dome H to a point nearthe bottom of the container l8. A shut-off valve 3! is preferablyprovided at the point where the conduit 38 enters the dome ll. Theconduit 30 within the container IE3 is preferably provided with anextension 32 which leads to a point near the bottom of the container Itat a substantial distance from the dome II. This is to insure thoroughmixture of the expanded and cooled incoming gas material with the bodyof liquid in the container IE3. The expansion valve 29 is preferably ofan automatically operated type, and it is adjusted according to theliquid level in the condenser 25. To this end there is provided a floatchamber 33 having a float therein connected to regulate the valve 29.The float chamber 33 is connected by conduits 3d and 35 with the upperand lower portions of the condenser 28, such that the levels of liquidin the float chamber 33 and condenser 25 are at the same height. If itshould be desired to by-pass the valve 29, a valved by-pass connection36 between conduits 28 and 38 may be provided, and for such purposeshut-off valves 37 and 38 at the inlet and outlet of the valve 29 arealso provided. The condenser 26 is also preferably provided with apressure gauge 39 and a vent valve 6t, which may be used to releasenon-condensable gases that may accumulate in the condenser 25 andinterfere with the operation thereof.

The compressor 25 is preferably directly coupled to a gas engine 4i.Such gas engine is provided with the customary air and gas mixing device42. For supplying the gas a branch connection d3, controlled by a valve44 is preferably provided from the vapor line 22. Interposed in theconnection 43 there may be a gas metering device 4-5 and otherauxiliaries, such as a first pressure reducing valve 45 discharging intoa chamber 4? in which gas is maintained at an intermediate pressure. Asecond pressure regulator 48 is provided to receive gas from the chamber4'! and discharge it into a surge chamber 49. The regulator 48 ispreferably made responsive to the pressure in the connection 50 betweenthe chamber 49 and the gas mixer 42, by a pressure connection 5|. At theinlet of the mixer 42 there is a control valve 52. The pressuremaintained in the chamber 49 is preferably only slightly aboveatmospheric pressure or it may be slightly below atmospheric pressurebecause the suction of the engine can draw gas from the chamber 29 asrequired, and when the engine does not run, or if the engine shouldstop, no gas would flow toward the mixer 42. It is also preferable toprovide a metering device in the vapor line 22 before the branch 43, forexample, an orifice 53 to which i connected a meter or indicating device54. The device 54 provides data to indicate the rate of circulation ofgas for refrigerating purpose, while the meter 45 will indicate theconsumption of gas by the engine 4! Only the consumption registered bythe meter 45 represents a loss of cargo.

A water circulating pump 55 is also driven by the engine 4!. The pump 55has a suction line 56 that leads from an intake 51 in the wall of abarge at the point below the normal water line and preferably near thebottom to draw in the coolest water. Interposed in the suction line 56there is preferably provided a strainer 58. A discharge line 59 of thepump 55 connects to the in, let 60 of the cooling water tubes in thecondenser 26, and a discharge line 5i conducts the used cooling waterfrom the water discharge outlet 62 of the condenser 26 to a dischargepoint outside of the barge at a distance from the intake line 5?.

In Figs. 2 and 3 is shown a preferred arrangement of four of thecontainers it upon a standard barge. The barge structure may include ahull B4 of more or less standard design havin a main deck 65, the tanksI!) being supported in the hull on suitable cradles, not shown, in suchmanner that the upper portions of the tanks protrude above the level ofthe main deck 65. At one end of the barge is a deck house 56, withinwhich the compressor 25, condenser 26 and engine 4! may be housed. Thedomes H of each of the containers ID are positioned so that they areclose together, and interconnecting manifolds are provided for theconduits connected to each dome. For example, the vapor line 22 may beconnected to each of the domes by four branches 22a, each of which mayhave a stop valve therein which is not shown in the interest ofclearness of the drawing. Such stop valves, however, may be' used sothat vapor can be drawn through the vapor line 22 from any one of thefour containers of which it may be desired to reduce the pressure, orany two or all of the containers can be opened to the vapor line 22 forreducing the pressure of all four containers simultaneously. Thepressuring line 30 may similarly be connected to each of the containersthrough branches and the charging and discharging lines i5 and 58 arealso connected to each of the containers. It will also be preferable toprovide a sheet metal cover over the containers Ill, which cover isjoined tightly to the main deck 65 to keep rain water and hydrocarbonvapor out of the hull.

In operation the containers are filled at a loading dock through thechargin line and vapors displaced from the containers may be returned tothe loading dock container through a connection to the vapor line. Arelatively small vapor space is left above the liquid in each containerto allow for liquid expansion up to the maximum working pressure ofabout p. s. i. If during the trip, the pressure of one or more of thecontainers should rise to about 75 p. s. i., the engine 4! will bestarted and the valves 31 and 23 opened in order to draw Vapor from thecontainer or containers having the high pressure. Starting of the enginemay be facilitated b providing a supply of compressed air which isconducted to the engine intake by a valve controlled line 58. The vaporswill be compressed by the compressor 25, liquefied under pressure in thecondenser 26 and with valve 36 closed and valves 37 and 38 open, theliquid will be expanded through valve 29 and then conducted throughconduit 38 and extension 32 into the container ii]. The liquid portionwill mix with the liquid in the container l8 and the portion of theliquid which is flashed into vapor by expansion (about one-quarter) willbubble up through the body of liquid [5 and thus create a movementthereof for circulating the body of liquid so that the cooling of itwill be uniform. When the body of liquid has been cooled enough to causethe pressure in the container to reduce to a preselected pressure below75 p. s. i., for example 65 p. s. i., the compressor may be shut down.

By designing the containers for 100 p. s. i. pressure a major reductionin weight of container is effected without incurring a largerefrigeration requirement. Thus a barge having four containers designedfor 100 p. s. i. and insulated as herein described would, to maintain apressure of about '75 p. s. i. during hottest summer conditions, requirethe operation of a '25 horsepower refrigeration compressor for onlapproximately of the time. Furthermorethe safety of shipment accordingto the invention is assured by the long time (approximately seven daysat hot summer conditions) for heat leak to increase the pressure from'75 p. s. i. to 100 p. s. i.

When the barge arrives at the unloading dock the liquid discharging linemay be connected to the receiving containers on shore and pressure isbuilt up to about 100 p. s. i. on the barge containers by addingsuperheated vapor through the pressuring line from a shore compressor.I'he propane is discharged from the containers ll) through line 18 bypressure difference preferably to the suction side of pumps at the shorestation, which pumps may force the liquid into permanent storage tanks.When the containers are empty of liquid the vapor pressure therein isdrawn down to about '75 p. s. land the containers are closed off. Apositive vapor pressure is always maintained in the containers.

While one embodiment of the invention has been disclosed and described,it is contemplated that modifications of the method and the apparatusmay be made and that some features of the invention may be employedwithout others without departing from the spirit and scope of theinvention.

What is claimed is:

1. A method of conserving a cargo of liquefied hydrocarbon gas, such asliquefied propane, in a large insulated container constructed for amaximum internal pressure of 100 s. i. and sub jected to atmospherictemperatures, which method comprises utilizing a small quantity of saidcargo as fuel for generating power, employing a major portion of saidpower for compressing a refrigerant, cooling said refrigerant by heatexchange with cooling water, utilizing such cooled refrigerant forcooling said cargo suificient to maintain the vapor pressure thereofclose to but not exceeding a predetermined working pressure below 100 p.s. i., and employing another portion of said power for pumping coolingwater for said heat exchange.

2. A method of transport-ing a cargo of liquefield hydrocarbon gas, suchas propane, in a large insulated container adapted to hold such cargounder superatmospheric.pressure on a marine vessel, such as a barge,over a waterway, which method comprises utilizing a small quantity ofvapor of said liquefied gas as fuel for generating power, employing amajor portion of said power for compressing gas material drawn from thevapor phase of said container, condensing said gas material by heatexchange with cooling water, expanding said condensed gas material andreturning same to said container to maintain a pressure thereinintermediate be tween the vapor pressure of said cargo at 115 F. andatmospheric pressure, and employing another portion of said power forpumping cooling water from said waterway for said heat exchange. I

3. Apparatus for transporting a cargo of liquefied hydrocarbon gas suchas propane, which comprises at least one large horizontally elongatedinsulated container constructed no heavier than required for internalpressures not exceeding about 100 p. s. i., a gas engine, means forsupplying a small quantity of the cargo to said gas engine for use as afuel therein to generate power, a compressor coupled to be driven bysaid gas engine, conduit means connecting the suction of said compressorto the vapor space of said container, a condenser connected to receivecompressed vapor from said compressor for liquefying the vapor, andmeans for expanding liquid from said condenser and delivering theexpanded material to said container to cool the cargo and maintain thevapor pressure thereof at a desired value below p. s. i., said means fordelivering expanded material opening into the liquid space of saidcontainer at a distance from the point of connection of said conduitmeans to the vapor space of said container.

4. Apparatus for transporting a cargo of liquefled hydrocarbon gas, suchas propane, which comprises at least one large insulated containerconstructed to hold such cargo under a pressure not exceeding about 100p. s. i. a marine vessel, such as a barge, supporting said container;said vessel also having thereon a gas engine, means for supplying asmall quantity of said cargo to said gas engine for use as fuel thereinto generate power, a compressor coupled to be driven by said gas engine,conduit means connecting the suction of said compressor to the vaporspace of said container, a condenser connected to receive compressedvapor from said compressor for liquefying the vapor, means for extendingliquid from said condenser and delivering the expanded material to saidcontainer to cool the cargo and maintain the vapor pressure thereof at adesired value below 100 p. s. i., and a pump coupled to be driven bysaid engine and connected to draw cooling water fromthe water supportingsaid vessel to force said cooling water through said condenser.

5. Apparatus for transporting a cargo of liquefied hydrocarbon gas, suchas propane, which comprises at least one large container constructed ofmetal having a thickness for a maximum internal working pressure notexceeding about 160 p. s. 1.; heat insulation around said containerequivalent on parts exposed to atmospheric temperature to about 4 inchesof cork; a refrigerating system including a refrigerant compressor and awater-cooled refrigerant condenser and constructed and arranged to coolsaid cargo when the vapor pressure thereof tends to exceed about '75 p.s. i. under conditions of atmospheric temperature as high as F.; anengine coupled to drive said compressor; and a water pump coupled to bedriven by said engine and connected for circulating the cooling waterthrough said condenser.

HAROLD E. il IOMPfSON.

REFERENCES CITED .n. following references are of record in the file ofthis patent:

UNITED STATES PATENTS

1. A METHOD OF CONSERVING A CARGO OF LIQUEFIED HYDROCARBON GAS, SUCH AS LIQUEFIED PROPANE, IN A LARGE INSULATED CONTAINER CONSTRUCTED FOR A MAXIMUM INTERNAL PRESSURE OR 100 P. S. I. AND SUBJECTED TO ATMOSPHERIC TEMPERATURES, WHICH METHOD COMPRISES UTILIZING A SMALL QUANTITY OF SAID CARGO AS FUEL FOR GENERATING POWER, EMPLOYING A MAJOR PORTION OF SAID POWER FOR COMPRESSING A REFRIGERANT, COOLING SAID REFRIGERANT BY HEAT EXCHANGE WITH COOLING WATER, UTILIZING SUCH COOLED REFRIGERANT FOR COOLING SAID CARGO SUFFICIENT TO MAINTAIN THE VAPOR PRESSURE THEREOF CLOSE TO BUT NOT EXCEEDING A PREDETERMINED WORKING PRESSURE BELOW 100 P. S. I., AND EMPLOYING ANOTHER PORTION OF SAID POWER FOR PUMPING COOLING WATER FOR SAID HEAT EXCHANGE. 